In the Garden:Pacific Northwest
May, 2009
Regional Report

The mushrooms and bittercress are planning a coup. It's time to fortify the lawn!

Time to Renew the Lawn

When we first seeded our lawn, it grew into an emerald green carpet with each blade identical to its closest neighbor. It was perfect -- something worthy of admiration, and so cool and inviting I would use any excuse to kick off my shoes and walk barefoot across the yard.

The honeymoon lasted four or five years. Even with regular feeding, watering, and mowing, native grasses invaded our beautiful turf and the lush, thick blades became fewer and farther between. Those adaptable natives were able to thrive where our hybrid turfgrass struggled to survive. Extended wet weather saturated the roots, flag football games compacted the soil, weeds erupted and spread their seeds, all the while creeping stealthily along the ground. We didn't even recognize the weeds were there until they had overtaken huge swaths of our lawn.

I know a thick, healthy turf will crowd out most weeds and those that do appear are easier to pull when the soil is in prime condition -- loose and rich with organic matter -- traits our turf no longer had. We knew without a doubt it was time to aerate our lawn.

As gardeners we never think twice about digging and hoeing our gardens to loosen compacted soils, but we forget we can provide the same benefits to our lawns with mechanical aeration. By loosening the soil, roots will gain a little room and have better access to air, water and fertilizer.

Aerating is Easy
Because you will use it only once every 5 or 6 years, you'll want to rent an aerator rather than purchase one. With a little experience you can treat a 2,000 square-foot lawn in about an hour, so you might consider sharing the aerator and rental fee with a few neighbors.

There are two types of aerators. Both are about the size of a tiller and easy to operate. The first punches a hole in the ground, pushing back soil to create a space. The other, called a core aerator, forces hollow shafts into the ground, removing plugs of sod, roots, and soil. This second type is what I prefer because it makes a hole without compacting the soil around it. The shafts are usually spaced to make 10 to 14 holes per square foot and will penetrate about 3 inches deep.

Give Roots a Little Breathing Room
Just about any lawn benefits from aeration, but several symptoms are a sure sign that aeration is required. When greens are not green enough, chances are fertilizer isn't reaching the roots. Aeration creates catch-basins to prevent fertilizer from running off during a rainstorm.

If your soil is hard and your grass is thin, roots need more space. If it feels as if you're walking on marbles, there's not enough oxygen in the soil, and earthworms have been forced to rise to the surface. Aeration gives both roots and earthworms a little more breathing room.

Let Plugs Remain
You can aerate at any time of the year and get good results, provided the ground isn't too dry. You can prepare the ground by watering thoroughly early in the morning before you rent the aerator. I think it's best to make two passes with the aerator: one right to left, the other front to back. If you're doing a slope and there's danger of the machine tipping on a side-to-side pass, go only in an up-and-down direction.

When plugs are removed by a hollow-shaft aerator, they should be left on the lawn. With each watering, the soil clinging to the plugs will wash back into the ground. Mowing will also reduce the size of the plugs (don't bag the clippings). As plant matter from the plugs is broken down by bacteria, it becomes an excellent food for your lawn.

After you've finished aerating the lawn, spread a thin layer of compost or sand over the entire area. Water from the hose, or rainfall, will work the material into the holes made by the plugs. You can overseed after aerating your lawn or you can just let the turf thicken up on its own. Either way, it will grow lush and thick in about 4 weeks and you'll be the envy of the neighborhood.